84 BULLETIN OF THE 



ward some, toward the top of the first branchial aperture. Behind the comer 

 of the taouth the oral makes a strong backward curve ; the tube is a long one ; 

 it crosses the symphysis and meets with the angular. Posteriorly the orbito- 

 nasal curves upward to meet the angular; the tube is elongate and nearly hori- 

 zontal. The nasal is long, sinuous, and almost transverse. Contrary to what 

 might be expected on a short snout, the median is long. As if reduction in 

 the length of the snout had proceeded faster than in that of the tubes, the 

 prenasals appear as if pushed back and folded on themselves ; each is turned 

 abruptly toward the side and bent into two folds. They unite with the 

 rostrals. 



Prominent distinguishing features in this shark are the caudal canals, scapu- 

 lar curves, complete oral, long suborbitals and orbito-nasals, and the folded 

 prenasals. Of the genera studied it approaches Scylliorhinus most closely. 



Scylliorhinus. 



Scylliorhinus caniculus (Plate XVII.) has scarcely any curvature in the later- 

 als, and they end with the column, not going down to the fibrous portion of 

 the caudal fin. 



A slight sinuosity affects the aural. The very short occipital is directed 

 toward the eye. Behind the fontanelle the cranials approach the median line 

 in a broad curve: in front of this, they turn abruptly out toward the edges of 

 the snout. Just before it joins the prenasal, there are several curves in the 

 rostral: in descending it runs forward, downward, inward, backward, and out- 

 ward. At the side of the nostril there is a prominent curve in the subrostral. 

 The suborbitals are longitudinal below the orbit ; at its forward edge they 

 pass down and backward to meet the short orbito-nasals. The nasals are 

 almost straight and transverse; the median is short; and the prenasals, sinu- 

 ous and moderately long, unite with the rostrals. From the angular the jugu- 

 lar curves up toward the upper edges of the gill opening, which it does not 

 reach. Behind each angle of the mouth there is a short disconnected oral. 



Heterodontus. 



On Heterodontus philippi (Plate XVIII.) the laterals diverge a little, behind 

 the occiput; farther back they are straight, without a curve over the anal fin, 

 until they reach the tail, above the lower lobe of which they descend to the 

 lower edge of the muscles. As it nears the end of the column, the canal 

 becomes a furrow. 



Lateral and aural form a continuous curve, and are connected with the cra- 

 nial and orbital, which form a similar curve, by a very short occipital. The 

 cranial bends are broad, but not at all deep. This is true also of the suborbital, 

 which reaches nearly a diameter in front of the orbit, then drops vertically on 

 the subrostral. Angular and jugular are both very short. The oral joins the 



